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The last universal ancestor (LUA, also called the last universal common ancestor, LUCA, the cenancestor or "number one" in slang
Slang

Slang is the use of highly informal words and expressions that are not considered standard in the speaker's dialect or language....
) is the most recent organism
Organism

In biology, an organism is any life thing . In at least some form, all organisms are capable of response to stimulus , reproduction, growth and developmental biology, and maintenance of homeostasis as a stable whole....
 from which all organisms now living on Earth descend
Common descent

A group of organisms is said to have common descent if they have a common ancestor. In modern biology, it is generally accepted that all living organisms on Earth are descended from a common ancestor or ancestral gene pool....
. Thus it is the most recent common ancestor
Most recent common ancestor

In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly Common descent....
 (MRCA) of all current life on Earth.






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Phylogenetic Tree


The last universal ancestor (LUA, also called the last universal common ancestor, LUCA, the cenancestor or "number one" in slang
Slang

Slang is the use of highly informal words and expressions that are not considered standard in the speaker's dialect or language....
) is the most recent organism
Organism

In biology, an organism is any life thing . In at least some form, all organisms are capable of response to stimulus , reproduction, growth and developmental biology, and maintenance of homeostasis as a stable whole....
 from which all organisms now living on Earth descend
Common descent

A group of organisms is said to have common descent if they have a common ancestor. In modern biology, it is generally accepted that all living organisms on Earth are descended from a common ancestor or ancestral gene pool....
. Thus it is the most recent common ancestor
Most recent common ancestor

In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly Common descent....
 (MRCA) of all current life on Earth. The LUA is estimated to have lived some 3.5 to 3.8 billion years ago
Timeline of evolution

This timeline of the evolution of life outlines the major events in the development of life on the planet Earth . For a thorough explanatory context, see the history of Earth, and geologic time scale....
 (sometime between the Basin Groups
Basin Groups

Basin Groups refers to 9 informal subdivisions of the lunar Pre-Nectarian lunar geologic timescale....
 and Paleoarchean
Paleoarchean

The Paleoarchean is a geologic era within the Archaean. It spans the period of time 3600 annum to 3200 Ma —the period being defined chronometrically and not referenced to a specific level in a rock section on Earth....
 era
Era

An era is a commonly used word for long period of time. When used in science, for example geology, eras denote clearly defined periods of time of arbitrary but well defined length, such as for example the Mesozoic era from 252 Ma?66 Ma, delimited by a start event and an end event....
s) .

Features


Based on the properties shared by all independently living organisms on Earth, it is possible to derive the features that the LUA must have had before it branched out:
  • The genetic code
    Genetic code

    The genetic code is the set of rules by which information encoded in genetic material is Translation into proteins by living cell s. The code defines a mapping between tri-nucleotide sequences, called codons, and amino acids....
     is based on DNA
    DNA

    Deoxyribonucleic acid is a nucleic acid that contains the genetics instructions used in the development and functioning of all known living organisms and some viruses....
    .
    • The DNA is composed of four nucleotide
      Nucleotide

      Nucleotides are molecules that comprise the structural units of RNA and DNA. Additionally, nucleotides play central roles in metabolism. In that capacity, they serve as sources of chemical energy , participate in cell signaling , and are incorporated into important cofactors of enzymatic reactions ....
      s (deoxyadenosine
      Deoxyadenosine

      Deoxyadenosine is deoxyribonucleoside and is considered a Derivative of the nucleoside adenosine, differing from the latter by the replacement of a hydroxyl group by hydrogen at the Nucleic acid nomenclature position of its ribose sugar moiety....
      , deoxycytidine
      Deoxycytidine

      Deoxycytidine is a deoxyribonucleoside. It is like cytidine, but with one oxygen atom removed....
      , deoxythymidine and deoxyguanosine
      Deoxyguanosine

      Deoxyguanosine is a Compound and a nucleoside. It is like guanosine, but with one oxygen atom removed at the 2' position of the ribose sugar . If a phosphate group is attached at the 5' position, it becomes Deoxyguanosine monophosphate....
      ), to the exclusion of other possible deoxynucleotides.
    • The genetic code is composed of three-nucleotide codons, thus producing 64 different codons. Since only 20 amino acids are used, multiple codons code for the same amino acids. These choices are arbitrary and are shared by all eukaryotes and prokaryotes. Archaea
      Archaea

      The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon . Archaea, like bacteria, are prokaryotic....
       and mitochondria use a similar code with minor differences.
    • The DNA is kept double-stranded by a template-dependent DNA polymerase
      DNA polymerase

      A DNA polymerase is an enzyme that catalyze the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best-known for their role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....
      .
    • The integrity of the DNA is maintained by a group of maintenance enzymes, including DNA topoisomerase, DNA ligase
      DNA ligase

      In molecular biology, DNA ligase is a special type of ligase that can link together two DNA strands that have double-strand break . The alternative, a single-strand break, is fixed by a different type of DNA ligase using the Complementary DNA as a template but still requires DNA ligase to create the final phosphodiester bond to fully repair...
       and other DNA repair
      DNA repair

      DNA repair refers to a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolism activities and environmental factors such as UV light and Radiation can cause DNA damage, resulting in as many as 1 million individual molecular lesions per cell pe...
       enzymes. The DNA is also protected by DNA-binding proteins like histones.
  • The genetic code is expressed via RNA
    RNA

    Ribonucleic acid is a type of molecule that consists of a long chain of nucleotide units. Each nucleotide consists of a nucleobase, a ribose sugar, and a phosphate....
     intermediates, which are single-stranded.
    • RNA is produced by a DNA-dependent RNA polymerase
      RNA polymerase

      RNA polymerase is an enzyme that produces RNA. In cell s, RNAP is needed for constructing RNA chains from DNA genes as templates, a process called Transcription ....
       using nucleotides similar to DNA with the exception of Thymidine, replaced by Uridine.
  • The genetic code is expressed into proteins. All other properties of the organism (e.g. synthesis of lipids or carbohydrates) are the result of protein enzymes.
  • Proteins are assembled from free amino acids by translation
    Translation

    Translation is the hermeneutics of the Meaning of a text and the subsequent production of an Dynamic and formal equivalence text, likewise called a "translation," that communicates the same message in another language....
     of an mRNA by ribosomes, tRNA and a group of related proteins.
    • Ribosomes are composed of two subunits, one big and one small.
    • Each ribosomal subunit is composed of a core of ribosomal RNA
      Ribosomal RNA

      Ribosomal RNA is the central component of the ribosome, the protein manufacturing machinery of all living biological cell. The function of the rRNA is to provide a mechanism for decoding mRNA into amino acids and to interact with the tRNAs during Translation by providing peptidyl transferase activity....
       surrounded by ribosomal proteins.
    • The RNA molecules (rRNA and tRNA) play an important role in the catalytic activity of the ribosomes
  • Only 20 amino acids are used, to the exclusion of countless non-standard amino acids; only the L-isomer
    Isomer

    In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
     is used.
    • Amino acids must be synthesized from glucose by a group of specialized enzymes; the synthesis pathways are arbitrary and conserved.
  • Glucose
    Glucose

    Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
     can be used as a source of energy and carbon
    Carbon

    Carbon is a chemical element with chemical symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalence?making four electrons available to form covalent bond chemical bonds....
    ; only the D-isomer
    Isomer

    In chemistry, isomers are compounds with the same molecular formula but different structural formulae. Isomers do not necessarily share similar properties unless they also have the same functional groups....
     is used.
    • Glycolysis
      Glycolysis

      Glycolysis is the metabolic pathway that converts glucose, C6H12O6, into pyruvate, C3H5O3-....
       goes through an arbitrary degradation pathway.
  • ATP
    Adenosine triphosphate

    This article is about the chemical used by cells as an energy carrier. For other uses, see ATP .Adenosine-5'-triphosphate is a multifunctional nucleotide, and plays an important role in cell biology as a coenzyme that is the "molecule unit of currency" of intracellular energy transfer....
     is used as an energy intermediate.
  • The cell is surrounded by a cellular membrane composed of a lipid bilayer
    Lipid bilayer

    A lipid bilayer is a thin membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around cell ....
    .
  • Inside the cell, the concentration of sodium
    Sodium

    Sodium is an element which has the symbol Na , atomic number 11, atomic mass 23 amu , and a common oxidation number +1. Sodium is a soft, silvery white, highly reactive element and is a member of the alkali metals within "group 1" ....
     is lower, and potassium
    Potassium

    Potassium is a chemical element. It has the symbol K , atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash, hence the name....
     is higher, than outside. This choice is arbitrary. This gradient is maintained by specific ion pumps.
  • The cell multiplies by duplicating all its contents followed by cellular division.


Hypotheses

When LUA was hypothesized, cladograms based on genetic distance
Genetic distance

Genetic distance is a measure of the dissimilarity of genetic material between different species or individuals of the same species. By comparing the percentage difference between the same genes or junk DNA of different species, a figure can be obtained, which is a measure of "genetic distance"....
 between living cells indicated that Archaea
Archaea

The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon . Archaea, like bacteria, are prokaryotic....
 split early from the rest of life. This was inferred from the fact that all known archaeans were highly resistant to environmental extremes such as high salinity, temperature or acidity, and led some scientists to suggest that LUA evolved in areas like the deep ocean vents
Black smoker

A black smoker or sea vent, is a type of hydrothermal vent found on the ocean floor. They are formed in fields hundreds of meters wide when superheating water from below Earth's Crust comes through the ocean floor....
, where such extremes prevail today. But archaeans were discovered in less hostile environments and are now believed by many taxonomists to be more closely related to eukaryotes than bacteria
Bacteria

The Bacteria are a large group of unicellular microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals....
, though this is still somewhat contentious.

It is possible that all of LUA's contemporaries became extinct
Extinction

In biology and ecology, extinction is the death of every member of a species or group of taxon. The moment of extinction is generally considered to be the death of the last individual of that species ....
 and only LUA's genetic heritage lived to this day. Or, as proposed by Carl Woese
Carl Woese

Carl Richard Woese is an American microbiologist and physicist. Woese is famous for defining the Archaea in 1977 by phylogenetic taxonomy of Svedberg ribosome RNA, a technique pioneered by Woese and which is now standard practice....
, perhaps no individual organism can be considered a LUA, but the genetic heritage of all modern organisms derived through horizontal gene transfer
Horizontal gene transfer

Horizontal gene transfer , also Lateral gene transfer , is any process in which an organism incorporates genetic material from another organism without being the Reproduction of that organism....
 among an ancient community of organisms. Another hypothesis to explain the paucity of alternative life forms is panspermia
Panspermia

Panspermia is the hypothesis that "seeds" of life exist already all over the Universe, that life on Earth may have originated through these "seeds", and that they may deliver or have delivered life to other habitable bodies....
, the inoculation of Earth by life carried on meteorite
Meteorite

A meteorite is a natural object originating in outer space that survives an impact with the Earth's surface. While in space it is called a meteoroid....
s.

See also

  • Timeline of evolution
    Timeline of evolution

    This timeline of the evolution of life outlines the major events in the development of life on the planet Earth . For a thorough explanatory context, see the history of Earth, and geologic time scale....
  • Common descent
    Common descent

    A group of organisms is said to have common descent if they have a common ancestor. In modern biology, it is generally accepted that all living organisms on Earth are descended from a common ancestor or ancestral gene pool....
  • Origin of life
  • Origins of cells
    Cell (biology)

    The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
  • Most recent common ancestor
    Most recent common ancestor

    In genetics, the most recent common ancestor of any set of organisms is the most recent individual from which all organisms in the group are directly Common descent....
  • Last Common Ancestor
    Last Common Ancestor

    A Last Common Ancestor is a term given to the most recent common ancestor of any two clades, for example species that came to be separated by a species barrier....